Internal combustion engines have tended to run rough at idle and low speeds, with smoother running at high speeds. It has been desired to improve the operation characteristics of such engines at their idle and lower speeds.
Furthermore, most internal combustion engines have been designed to operate on gasoline. However, less volatile fuels such as kerosene or the like would be preferable in many instances due to their lower cost. Previous attempts to utilize kerosene have not been entirely successful, especially in water cooled marine engines, because the mixture of air and lower octane fuel was not hot enough at idle and slow speeds to ignite in the combustion chamber.
One known manufacturer has built an engine which uses two fuel systems. Gasoline is used when the engine is started, at idle and at part throttle. As the throttle is opened wider, with accompanying hotter operation, kerosene gradually supplants the gasoline.
In addition, kerosene burning farm tractor engines have run the intake manifold inside of the exhaust manifold to heat the air-fuel mixture.